Humidifier casing



FIG. 1 is a front and left side perspective view of a humidifier casing showing our new design;

FIG. 2 is a left side elevation view thereof;

FIG. 3 is a right side elevation view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a front elevation view thereof; and

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a humidifier casing, as shown. 